The Federal Communications Commission (FCC) originally conceived license exempt bands to provide a no-cost slice of public access spectrum with only two provisions. First, the transmitter may cause no harmful interference to any nearby licensed services, and secondly, any receiver in this band must be able to accept any interference that may be present. An example of license exempt bands may be industrial, scientific and medical (ISM) radio bands, which were reserved for the use of the wireless spectrum for USM purposes other than communications. The allocation of the ISM bands may differ in each nationality based on different regulations. Another example may be the Unlicensed National Information Infrastructure (UNII) spectrum, which may be used by Institute of Electrical and Electronics Engineers (IEEE) 802.11a devices and by many wireless Internet service providers (ISPs). The term license exempt may be used to refer to unlicensed and lightly licensed spectrum.
In the United States, 408 MHz of spectrum from 54 MHz to 806 MHz may be allocated for television (TV). A portion of that spectrum may be redeveloped for commercial operations through auctions and for public safety applications. The remaining portion of the spectrum may remain dedicated for over-the-air TV operations. However, throughout the United States, portions of that spectrum resource may remain unused. The amount and exact frequency of unused spectrum may vary from location to location. These unused portions of spectrum may be referred to as TV White Space (TVWS).
The FCC devised the TVWS with a slightly different set of regulations, which cannot be equated to either unlicensed or license exempt. These lightly licensed regulations are imposed on a major portion of the TVWS spectrum and require the primary users to purchase a license, which provides them first rights to transmit in the band. No one is allowed to interfere while a primary user is operating, but once the existing primary user is off the air, any other primary user with a license may begin to use the channel. Thus, a primary user gets exclusive licensed use of a channel for a period of time. During this time it needs to be registered with a centralized database, whose entries are mapped on a geographical basis. If no primary user is registered with the database, secondary users may access the spectrum in an unlicensed manner.
Wireless telecommunication equipment operates on licensed bands to communicate with cellular networks. As the demand for additional spectrum is constantly on the rise, it is would be beneficial to enable users to seamlessly and opportunistically roam across various wireless access networks in the search for more throughput or cheaper bandwidth. Secondary utilization of unused spectrum, be it unlicensed, lightly licensed, or licensed, requires efficient detection and sharing without harmful interference with other users. Methods are therefore needed to enable wireless telecommunication equipment to communicate via license exempt bands as well as licensed bands.